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© Published under licence by IOP Publishing Ltd. The area of the Volga-Ural oil and gas basin belongs to the "old" oil and gas bearing regions. The most part of easily recoverable reserves of large and unique oil fields already have been developed within the area. Therefore, super-viscous oil reservoirs, natural bitumen deposits and shale hydrocarbons seized the attention of local petroleum geologists. Tatarstan is a classic example in that sense. The Republic of Tatarstan is a leader in the development of heavy oil resources, a leader in the degree of knowledge of natural bitumen accumulations, as well as a leader in technological readiness for their development. In the depths of Tatarstan, there are more than 450 fields of ultra-viscous oil and natural bitumen with reserves ranging from 2 to 7 billion tons of this type of hydrocarbons. However, their industrial development due to low profitability is slow. To solve the problem, it is necessary to search for and commercialize economically viable technologies for the production, transportation and processing of hydrocarbons, which take into account its features and do not require increased energy and other material costs. Therefore, the search for the right unconventional hydrocarbons production concept is an urgent problem of our time.

© Published under licence by IOP Publishing Ltd. This article presents the distribution of natural bitumen in the sediments of the Kazan tier of the middle Permian. Natural bitumens, concentrated in the Permian sediments of the Republic of Tatarstan, occur at shallow depths and are heavy, highly viscous, hypergenically converted oils. In the tectonic relation, the area of maximum Kazan bitumen occurrence is confined to the Melekess depression and the adjacent slope of the South Tatar arch.

© Published under licence by IOP Publishing Ltd. Authors of the article identified the influence of sedimentation conditions on reservoir thickness and the patterns of change in reservoir properties of superviscous oil field from the following three zones of the sandstone sequence of the Sheshminsky horizon: Northern, Southern and Central identified by PJSC Tatneft and prepared for initial development. The following relationships have been investigated: Open porosity relation with bitumen content (by weight and by volume), open porosity relation with carbonate content, open porosity relation with bulk density, carbonate content relation with bulk density, bitumen content (by weight and by volume) relation with carbonate content, and also bitumen content relation with their depth. The revealed patterns of changes in reservoir properties and bitumen content within the sandstone sequence can be the result of not only changing conditions of sedimentation, but also the result of post-sedimentation processes resulting in calcitization or redistribution of carbonate cement in the rock under the influence of aggressive products (oxidation, biodegradation) of oil deposits destruction.

© 2019, International Multidisciplinary Scientific Geoconference. All rights reserved. Geodynamic processes, which play an important role in the formation of oil fields in the central regions of the Ural-Volga region, were also leading in creating conditions for their destruction. There were several stages of generation, migration, accumulation of oil and the destruction of its deposits, which determined the frequency of their formation and destruction. According to the results of the geochemical study of organic matter, the most ancient stages of the formation of hydrocarbon deposits are recorded in the pre-Paleozoic (Riphean) sediments. According to the ideas of ontogenesis of oil, geodynamic processes determined the following main factors of the formation of clusters of superviscous oil and natural bitumens in the Permian sediments of the Melekessky region of bitumen accumulation: genetic factor-determines the generation of hydrocarbons. The formation of Permian superviscous oil and natural bitumen is associated with the presence of oil deposits in the Devonian and Carboniferous sediments. The main strata with the source potential in the Devonian system are clay-carbonate of the domanicoid facies; geodynamic factor-characterizes the modern and paleostructural plans, migration and accumulation of hydrocarbons, the stages of formation of deposits; hydrogeological factor manifests itself in two aspects: during the formation of oil deposits-the initial migration of hydrocarbons is carried out as part of the aqueous phase; at the destruction of deposits-under the influence of infiltration waters saturated with oxygen and microorganisms, hypergenesis processes occur. As a result reduction of the of the oil (bitumen) hydrocarbon composition and, in general, an increase in the tar-asphaltene components. Thus, the development of oil is completed with bitumen formation. These processes, being characterized by an evolutionary orientation in their development, take place in

© 2016, International Journal of Pharmacy and Technology. All rights reserved.During paleogeographic studies the identification of channel, deltaic and avandeltaic environments of sedimentation is obstructed. Experience shows that their definition according to the granulometric composition of constituent deposits is not a sufficient basis for the reference to the category of continental facies. To do this, we should attract some indirect evidence, for example, the drawing of paleo drain network, the geometry of sandbodies and the configuration of basal and lateral contacts, etc. The performed studies demonstrated the transformation of sandbodies due to the nonuniform compressibility of clay and sand rocks, causing to the formation of various pseudo-structural elements in the form of bends and folds. Therefore, during the identification of formation conditions for clastic natural reservoirs the adjustment of trap forms is needed for the processes of enclosing clay rock compaction.

© 2016, International Journal of Pharmacy and Technology. All rights reserved.During paleogeographic studies the identification of channel, deltaic and avandeltaic environments of sedimentation is obstructed. Experience shows that their definition according to the granulometric composition of constituent deposits is not a sufficient basis for the reference to the category of continental facies. To do this, we should attract some indirect evidence, for example, the drawing of paleo drain network, the geometry of sandbodies and the configuration of basal and lateral contacts, etc. The performed studies demonstrated the transformation of sandbodies due to the nonuniform compressibility of clay and sand rocks, causing to the formation of various pseudo-structural elements in the form of bends and folds. Therefore, during the identification of formation conditions for clastic natural reservoirs the adjustment of trap forms is needed for the processes of enclosing clay rock compaction.